Presses have many uses, one of the most popular being to clamp mold parts together in an injection molding apparatus. In a conventional injection molding apparatus a press section is disposed behind a plastic injection section. The press includes a moving platen which is forced toward a stationary platen by at least one actuator, usually a hydraulic cylinder mounted at the rear of the apparatus. The actuator bears against a stationary rear frame or "spider", which supports upper and lower pairs of guide bars that maintain the moving and stationary platens (and thus the mold parts) in precise alignment as the actuator forces the moving platen toward the stationary platen and into the clamping position.
Typically a hydraulic press is used in an injection molding apparatus, due to the very high forces required to properly clamp the mold parts together. In a conventional hydraulic actuator the hydraulic cylinder must be longer than the length of a full stroke of the piston and must be oriented in the direction of the stroke. Since the injection molding apparatus occupies the space in front of the press, the hydraulic cylinder is conventionally mounted to the rear of the press and thus a large clearance is required behind the operative clamping portion of the press in order to accommodate the cylinder.
Moreover, in a conventional hydraulic press the hydraulic cylinder serves the sole purpose of actuating the moving platen, and separate guide bars are used to maintain the moving and stationary platens in precise alignment. The use of separate structures for these purposes results in an expensive and heavy apparatus which makes poor use of available space.
It would accordingly be advantageous to provide a hydraulic press in which the actuating cylinders can be reduced in length and contained within the operative clamping section of the press, to significantly reduce the space requirements of the overall apparatus and thus allow plastics fabricators to utilize production facilities more efficiently.
It would also be advantageous to provide a press which combines the actuating and platen alignment functions of the press into the same structure, to reduce the weight and cost of the apparatus.
It would also be advantageous to provide a press that operates in two directions, taking advantage of the reciprocating motion of the actuator, to provide two injection molding cycles within a single press cycle.